You need the following information to link your account: API Key, Ad Unit, Ad Unit ID.
Reporting API Access Code: Read about how to get an API Access Code here.
API, Ad Unit and Ad Unit ID: On your Dashboard choose Manage, then click on Apps & Ad Units. API Key is in the third column. In order to find Ad Unit and Ad Unit ID, in the App Name column click on the app you need information about. In the block that appears below find Ad Unit and Ad Unit ID.